Cathode ray tube gun having a second grid with an effective thickness



Dec. 27, 1966 G. A. BURDICK ETAL 3,

CATHODE RAY TUBE GUN HAVING A SECOND GRID WITH AN EFFECTIVE THICKNESS Filed June 4, 1963 2 Sheets-Sheet l i liil l liiil mmum 5 ii 5 Adz INVENTORS Glen ABurd/ck BY T/Qyd K.Co// 'ns H2 w/ i'jlfw F4,- ATTORNEY Dec. 27, 1966 G. A. BURDICK ETAL 3, 9

CATHODE RAY TUBE GUN HAVING A SECOND GRID WITH AN EFFECTIVE THICKNESS 2 Sheets-Sheet 2 Filed June 4, 1965 INVENTORS Glen A. Bard/ck F/oyd K. Call/r25 fol/VA Half/Il [III]! II.

ATTORNEY United. States Patent CATHODE RAY TUBE GUN HAVING A SECOND GRID WITH AN EFFECTIVE THICKNESS Glen A. Burdick, Waterloo, N.Y., and Floyd K. Collins, Ottawa, Ohio, assignors to Sylvauia Electric Products Inc, a corporation of Delaware Filed June 4, 1963, Scr. No. 285,384 6 Claims. (til. 313-82) This invention relates to electron discharge devices and more particularly to cathode ray tubes adapted to be cathode driven.

A conventional type of cathode ray tube commonly employed in television receiver applications achieves high transconductance by utilizing a low G cathode driven electron gun wherein the second or screen grid is operated at a relatively low DC voltage and the video signal is applied to the cathode.

The term transconductance as used herein refers to the change of anode current with reference to the change of cathode voltage AIaJAEk.

Cathode drive operation is equivalent to modulating all of the other electron gun elements with respect to the cathode. Thus a cathode ray tube utilizing an electron gun of this nature has desirable drive characteristics since less video drive is required to achieve cutoff when the signal is applied to the cathode than when applied to the control grid. The modulating voltage has increased effect upon the emission and cutoff when the gun elements effectively drawing emission from the cathode, are operated at relatively low voltage levels. Thus utilization of a low G voltage is advantageous in tube operation since a given change in the voltage between the second grid and the cathode is more effective when the second grid is operated at 100 volts positive or lower. In addition, it is advantageous to provide a second grid that ex- =hibits more effectiveness in drawing emission than does the higher-voltage-operating anode. To accomplish this it is desirable to have the second grid provide effective shielding or screening for the first grid cathode region.

In an effort to achieve the desired drive characteristics of cathode driven low G operation, various electron gun parameters have been employed with differing degrees of accomplishment.

Gun design modifications, while achieving certain degrees of success, have introduced aggravating problems. The reduction of the second grid operating voltage and the realization of improved screening action to achieve a reasonable peak or zero bias emission level both, in practical usage, require very close first grid to cathode and first grid to second grid spacings. These conditions complicate electron gun construction. Thus there is a practical manufacturing limit to the improvement in drive characteristics which can be adequately accomplished by this approach. Increasing the diameter of the first grid aperture enables the use of increased first grid to cathode and first grid to second grid spacings but a degradation in focussed spot size and resolution are undesirable resultants. Another approach to achieve satisfactory drive characteristics embodies the use of a substantially smaller diametered second grid aperture with reference to the first grid aperture. This arrangement is very critical for electrode placement as misalignment of the grid apertures will resultant in undesirable interception of the beam current by the second grid.

Accordingly, it is an object of the invention to reduce the aforementioned disadvantages and to achieve improved hig-h transconductance and small spot size in a cathode driven cathode ray tube of economic fabrication.

Another object is to produce a cathode ray tube having increased screening effect of the second grid on the anode field.

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An additional object is to provide a cathode ray tube wherein the uniformity of the focussed image is improved.

A still further object is to provide a gun structure for a cathode ray tube wherein the criticality of electrode spacings is reduced.

The foregoing objects are achieved in one aspect of the invention by the provision of a cathode ray tube incorporating an electron gun assembly including a cathode, a first grid and a second grid. The first grid has an end wall formed to provide an aperture coaxially aligned with the cathode. The thickness of the end wall immediately surrounding the first grid aperture is less than twenty percent of the aperture diameter. The second grid is of dual diaphragm construction having coaxially aligned proximal and distal apertures with respect to the first grid aperture. The proximal second grid aperture has a diameter at least equal to that of the first grid aperture, while the diameter of the distal second grid aperture is at least equal to that of the proximal second grid aperture.

For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection withthe accompanying drawings in which:

FIG. 1 is a plan view of a cathode ray tube;

FIG. 2 is an enlarged sectional view of the electron gun structure utilized in the tube shown in FIG. 1;

FIG. 3 is a detailed view portraying the cathode, first grid and second grid structures of the electron gun shown in FIG. 2; and

FIGS. 4 to 8 are sectional views showing modifications of the second grid apertures.

For purposes of illustration there is shown in FIG. 1, a unipotential electrostatically-focussed cathode-driven cathode ray tube of the type conventionally employed'as a television picture tube. The cathode ray tube 11 comprises an envelope 13 wherein the electron gun 15 is spacedly mounted relative to the fluorescent screen 17. The electron gun provides the source, acceleration, control and focussing of the electron beam 19 which is controllably deflected by externally positioned coils 21 to impinge upon the screen 17 and provide an image display raster thereupon.

The electron gun 13-, as shown in FIG. 2, comprises a cathode assembly 23 which includes a substantially cylindrical sleeve 25 having electron emissive material 27 deposited on the closed end thereof. An electric heater 29, positioned within sleeve 25, provides the heat necessary for the activation of electrons from emissive material 27. Spaced from the cathode, in proper alignment along the path of electron travel, is a first grid 31, a second grid 33, an electron accelerating anode and a unipotential electrostatic focussing assembly 37.

The electron beam 19 is electrostatically focussed by assembly 37 to provide a spot of minimum diameter at the point of impingement on the fluorescent screen 17. This focussing assembly 37 includes two spaced lens cups 39 and 41 having respectively aligned apertures 43 and 45 formed in the respective adjacent end walls thereof. A lens ring 49 spacedly surrounds lens cups 39 and 41 at substantially their aperture regions. The focussing assembly 37 functions to control the electron beam 19 emanating from the cathode emissive material 27 in a manner to produce convergence as a discretely defined small diametered spot on the fluorescent screen 17.

With reference to specific nomenclature as used in this description, the term aperture may be defined as substantially the functional or minimum opening formed by the periphery of the bore. In accordance therewith, the term aperture diameter refers to the respective diametrical dimension considered of primary importance to 3. the intended function, and the term. effective aperture thickness has reference to the functional depth of the bore or conjunctive bores comprising the respective grid structure.

- In referring to FIG. 3, the first grid 31 is formed substantially as a cylinder having an axial bore therein forming an aperture, 51 spaced from and aligned with cathode electron emissive material 27. The end wall 53 of the first grid is concavely coined or operated upon by other means to reduce the thickness of the end wall immediately surrounding the aperture 51. The coining procedure forms a recess in the first grid end wall 53 on the surface farthest removed from the cathode'and facing the second grid 33. The second grid 33, which may be of cylindrical formation but not necessarily so, has two dual diaphragms serving as end walls: a proximal diaphragm 55 positioned in spaced adjacency with the end wall 53 of first grid 31, and a distal diaphragm oriented relative to proximal diaphragm 55 being farther removed from the first grid 31. Both the proximal and distal diaphragms having respective bores forming apertures 59 and 61 therein are coaxially aligned with the first grid aperture 51. The diameter of the proximal second grid aperture 59 (Ad2) is at least equal to the diameter of the first grid aperture 51 (Adi), and the diameter of the distal second grid aperture 61 (Ad2.') is at least equal to the diameter of the proximal aperture related thereto; i.e. AdZZAdZgAdl.

It has been found that related aperture diameters and eifective thicknesses are important in fabricating a low G high transconductance cathode driven cathode ray tube. The dimensions of the apertures and the spacings as shown in FIG. 3 illustrate a construction which provides desirably efficient performance.

The end wall 53 of the first grid 31 has a thickness of .007 inch which is reduced as by concave coining to an effective thickness (Etl) of .0025 inch in the area immediately surrounding the aperture 51. The diameter of the first grid aperture 51 (Adi) is .031 inch. It has been found that the effective thickness of the first grid aperture (Etl) should preferably be less than 20% of its diameter (Adi); i.e. Etl .20Ad1. It is evident that the thickness diameter ratio is well satisfied in the dimensions herein presented. K

The proximal diaphragm 55 of secondgfgrid 33 is .010 inch in thickness of which the area immediately surrounding the aperture is dimpled concavo-convexly toward the first grid concavely coined axial region adjacent aperture 51. The proximal aperture 59 is coaxially aligned with the first grid aperture and has a diameter (Ad2) of .032 inch being larger than the first grid diameter (Adl). As previously mentioned, it has been found that the proximal aperture 59 should have a minimum diameter at least equal to the diameter of the first grid aperture 51: AdZgAdl.

There is associated with the second grid proximal diaphragm 55 a second grid distal diaphragm 57 of .007 inch thickness having an axially positioned aperture 61 therein which is in coaxial alignment with the first grid and proximal apertures 51 and 59 respectively. The diameter of the distal aperture 61 (Ad2') is .036 inch which is diametrically larger than the proximal aperture 59', thus conforming to the teaching of the inventionwherein the minimum diameter of the distal aperture of the sec-ond grid should be at least equal to the proximal aperture diameter of that structure: AaZ'ZAdZ. This minimizes the possibility of the second grid undesirably intercepting the electron beam and thereby reduces the criticality of the second grid 33 alignment relative to the first grid 31.

Through experimentation, it has been resolved that the effective aperture thickness of the second grid (Et2); i.e. the distance or thickness measured between the proximal aperture surface nearest the first grid and the distal aperture surface farthest from the first grid, is also a factor related to the aperture diameter in conjunctively determining the efliciency of the screening effect of the second grid on the anode field. The effective thickness of the second grid aperture (E12), so determined, should be greater than .5 time the the diameter of the distal aperture (AdZ) therein: Et2 .5Ad2'. As shown in FIG. 3, the second grid 33 elfective thickness is .028'inch.

Pertinent inter-related longitudinal electrode spacings are also indicated in FIG. 3. The positioning of the cathode assembly 23 within the first grid structure 31 spaces the electron emissive material 27, disposed on the end of cathode sleeve 25, .0035 inch from the internal surface of the first grid end wall 53. Removed from the adjacency of the aperture region the proximal end wall or diaphragm 55 of the second grid 33 is spaced .0095 inch from the end Wall 53 of the first grid 31. Since the proximal aperture 59 is concavo-convexly formed to extend toward concavely coined first grid aperture 51 the spacing therebetween is in the order of .003 inch.

It has been found that the spacings and dimensions of anode 35 and the focussing assembly electrodes extending therebeyond are not critical to the invention. Nevertheless, these electrodes are assembled as necessary parts of the electron gun structure to provide adequate focussing of the electron beam 19 on the screen 17.

While FIG. 3 illustrates one embodiment of the invention wherein the effective aperture thickness of the second grid 33 (B12) is effected by the concave-convex dimpling of the proximal end wall or diaphragm 55 relative to the adjacent distal end wall or diaphragm 57, other means for achieving the desired effective aperture thickness for the second grid (1322) may be accomplished as shown in FIG- URES 4 to 8.

In FIG. 4 there is shown a second grid 62 having an end wall or diaphragm 63 of which the thickness is equal to the effective aperture thickness of the grid (Et2). Axially therethrough is a frusto-conical bore 76 having concentric proximal 65 and distal 67 apertures in coaxial alignment with the first grid aperture 51. The respective diameters of the proximal and distal second grid apertures Ad2 and Ad2, for FIGURES 4 through 8 have the same relationships as heretofore described for FIG. 3:

AdzgAdi and Adz'gAdz FIG. 5 shows a second grid 69 having the end wall 70 composed of two contiguous diaphragms 70 and 73 wherein an axial frusto-conical bore 78 has a proximal aperture 75 and a distal aperture 77. The effective second grid aperture thickness being Et2. If so desired, the end wall or diaphragm 70 could be formed of a plurality of laminations to build up the desired effective aperture thickness. The relationship of the proximal and distal apertures 75 and 77 would remain as described, the bore therebetween being diametrically progressive.

There is shown in FIG. 6, a proximal second grid diaphragm 79 having a bore forming an aperture 80 which is discretely spaced from a distal diaphragm 81 having a bore forming an aperture 82 to provide the desired second grid effective aperture thickness E2. The frusto-conical bore eifect 76 and 78 as evidenced in FIGURES 4 and 5, is essentially retained in FIG. 6 by the beveled proximal bore 83, and the beveled distal bore both of which progressively expand in the direction of travel of the electron beam 19 from the cathode emissive surface 27 to the point of impingement on the screen 17.

FIGURE 7 illustrates aperture bore variations that are modified embodiments of those shown in FIG. 5 wherein the numerical prime designations indicate similar structural elements. Substantially cylindrical type proximal bore 83' and distal bore 85', in proximal diaphragm 71' and distal diaphragm 73' respectively, replace the frustoconical slope 78 shown in FIG. 5.

FIGURE 8 shows the second grid proximal diaphragm 79 in spaced relationship with distal diaphragm 81'. Re

spective proximal and distal aperture bores 83 and 85 being substantially cylindrical in contours.

A cathode driven cathode ray tube of thetype described herein exhibits relatively high transconductance AIa/AEk. As indicated in FIG. 2 the potential values involved exemplify excellent drive characteristics. The gun design, especially the first grid and second grid portions, enhances the achievement of the desired drive characteristics with minimized electron beam interception by the second grid structure. Thus the criticality of electrode spacings is reduced, increased screening eifect of the improved second grid on the anode field is provide-d and uniformity of the focussed image is improved. In addition, the aforementioned facets of achievement are feasibly realized in an improved gun structure of economic fabrication.

While there has been shown and described What is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention as defined by the appended claims.

What is claimed is:

1. A cathode ray tube utilizing an electron gun having a cathode and sequential electrodes formed and spaced therein to provide the source, acceleration, control and focussing of an electron beam on an image screen comprising in combination:

a first grid positioned relative to said cathode having an end Wall formed with a bore therein to provide a first grid aperture ooaxially aligned with said cathode; and

a second grid positioned relative to said first grid having an end wall construction spaced from said first grid end wall and formed with concentric proximal and distal apertures therein coaxially aligned with said first grid aperture, said proximal second grid aperture being adjacent said first grid aperture and having a minimum diameter larger than the diameter of said first grid aperture, said distal second grid aperture being farthest removed from said first grid aperture and having a minimum diameter larger than said diameter of said proximal second grid aperture, said second grid having an effective aperture thickness measured between the proximal aperture surface nearest said first grid aperture and the distal aperture surface farthest from said first grid aperture said effective thickness being greater than .5 time the diameter of said distal second grid aperture. 2. A cathode ray tube electron gun according to claim 1 wherein said second grid end wall construction is comprised of dual diaphragms in the form of adjacently positioned proximal and distal diaphragm members having said proximal and distal apertures therein.

3. A cathode ray tube electron gun according to claim 2 wherein said first grid end Wall surface farthest removed from said cathode and immediately surrounding said first grid aperture is concavely coined to a reduced effective thickness and wherein said proximal aperture portion of said second grid proximal diaphragm is dimpled concavo-convexly toward said first grid coined aperture, and wherein said distal diaphragm with said distal aperture therein is substantially planar.

4. A cathode ray tube electron gun according to claim 2 wherein said proximal and distal aperture-s are formed as frusto-oonical bores expanding in the direction of travel of said electronbeam.

5. A cathode ray tube electron gun according to claim 4 wherein said frusto-conical distal second grid aperture has a minimum aperture diameter at least equal to the maximum diameter of said frusto-conical proximal second grid aperture.

6. A cathode ray tube electron gun according to claim 2 wherein at least said aperture portions of said proximal and distal diaphragms are in substantially spaced apart relationship.

References Cited by the Examiner UNITED STATES PATENTS DAVID J. GALVIN, Primary Examiner.

P. C. DEMEO, Assistant Examiner. 

1. A CATHODE RAY TUBE UTILIZING AN ELECTRON GUN HAVING A CATHODE AND SEQUENTIAL ELECTRODES FORMED AND SPACED THEREIN TO PROVIDE THE SOURCE, ACCELERATION, CONTROL AND FOCUSSING OF AN ELECTRON BEAM ON AN IMAGE SCREEN COMPRISING IN COMBINATION: A FIRST GRID POSITIONED RELATIVE TO SAID CATHODE HAVING AN END WALL FORMED WITH A BORE THEREIN TO PROVIDE A FIRST GRID APERTURE COAXIALLY ALIGNED WITH SAID CATHODE; AND A SECOND GRID POSITIONED RELATIVE TO SAID FIRST GRID HAVING AN END WALL CONSTRUCTION SPACED FROM SAID FIRST GRID END WALL AND FORMED WITH CONCENTRIC PROXIMAL AND DISTAL APERTURES THEREIN COAXIALLY ALIGNED WITH SAID FIRST GRID APERTURE, SAID PROXIMAL SECOND GRID APERTURE BEING ADJACENT SAID FIRST GRID APERTURE AND HAVING A MINIMUM DIAMETER LARGER THAN THE DIAMETER OF SAID FIRST GRID APERTURE, SAID DISTAL SECOND GRID APERTURE BEING FARTHEST REMOVED FROM SAID FIRST GRID APERTURE AND HAVING A MINIMUM DIAMETER LARGER THAN SAID DIAMETER OF SAID PROXIMAL SECOND GRID APERTURE, SAID SECOND GRID HAVING AN EFFECTIVE APERTURE THICKNESS MEASURED BETWEEN THE PROXIMAL APERTURE SURFACE NEAREST SAID FIRST GRID APERTURE AND THE DISTAL APERTURE SURFACE FARTHEST FROM SAID FIRST GRID APERTURE SAID EFFECTIVE THICKNESS BEING GREATER THAN .5 TIME THE DIAMETER OF SAID DISTAL SECOND GRID APERTURE. 